The present invention relates, as indicated, to stacking apparatus for signatures from a printing press, for example, and more particularly to a stacker of the compensating type. Books, newspapers, magazines, phamphlets, etc. involving folded over sheets or stapled sheets or a combination of both often have one edge which is somewhat thicker than the opposite edge. When such "signatures" are stacked in the same attitude, the thicker edges build up faster than the free edges to a point where the stack is unstable and difficult to control and handle. To solve this problem, compensating stackers have been provided which are characterized by a channel-way or stacking frame formed of aligning bars extending between an elevated signature delivery point and a turntable receiving plate, the latter being rotatable through 180.degree. on command. Within the stacking frame and intermediate its ends there is provided a temporary platform which gathers a predetermined number of signatures as they exit from the delivery apparatus, such as for example, a tape conveyor. The tape conveyor leads to the stacker from a prior operation, e.g. a trimmer. The signatures are delivered in succession and all in the same attitude. Thus, as the pile portion builds on the temporary platform toward the predetermined number, the thicker edges are all piled one above the other. When the predetermined number in the pile portion is reached, the temporary platform releases or carries the pile portion to a turntable which accepts the pile portion. The turntable is then rotated through 180.degree..
In the meantime the same, or a different temporary platform is reestablished in the stacking frame to intercept the next successive signatures from the conveyor until another pile portion of equal size to the prior pile portion is accumulated. This pile portion is then released or carried for deposit on top of the preceding pile portion which by now has been rotated through 180.degree.. However, the superimposed thicker edges of the succeeding pile portion are now disposed over the relatively thinner superimposed edges of the next preceding pile portion. In this manner, a compensated stack of a plurality of pile portions each having a predetermined number of signatures therein is built up. When the stack contains a desired total number of signatures (which is a multiple of the predetermined number of signatures in each pile portion) it is ejected from the turntable for further handling, e.g. tying, wrapping, or boxing, for example.
The devices of the present invention are compensating stackers which operate in the same manner as above generally described, but include improved means particularly for releasing a pile portion formed on a temporary platform, and reestablishing the platform.
Representative of prior art in this field are the following: U.S. Pat. No. 1,560,113 to Sandaljian shows a sheet stacking machine with one form of a temporary platform. U.S. Pat. No. 3,568,578 shows a stacker for a rolling press providing a pair of receiving plates in the middle of the channel-way or passage, alternately insertable into the passage and lowered with the signatures and withdrawable at the lower end of the passage and elevatable along the outside of the passage. U.S. Pat. No. 3,880,421 to Muller shows a temporary platform or "aligning members" which swing apart causing the stack formed thereon to drop. U.S. Pat. No. 3,122,230 shows a book dropping apparatus utilizing counter rotating spirals.
Other prior art of interest in connection with apparatus of the type here contemplated include German offenlegungsschrift No. 1,951,506, utilizing a pair of coopera g "star" wheel elements to form a temporary platform; U.S. Pat. Nos. 2,205,767; 2,759,615; 2,886,929; 3,044,772 for an ejection system operated by an air cylinder; U.S. Pat. Nos. 3,486,425; 3,414,257 for collating apparatus; U.S. Pat. Nos. 3,599,965; and 3,768,382.
Among known mechanisms for providing a temporary platform and depending on simultaneously counter-rotable parallel shafts having inwardly extending fingers, a principal example is shown in the aforesaid German offen. No. 1,951,506. Here the rotating members have a "star" wheel configuration of a plurality of radially extending fingers. Opposing fingers of the opposing star wheel elements cooperate to form a horizontal temporary platform on which a pile portion may form. In the subject German reference, the fingers are 120.degree. apart. It has been found that with platform forming elements of this type, the fingers of the next 120.degree. sector when moving into a platform forming position may strike the edge of the pile portion and damage one or more signatures. By utilizing a platform forming element in accordance herewith, this problem is entirely avoided. The fingers forming the temporary platform in the improved devices extend from a single longitudinal element of the parallel shafts and rotate through 360.degree. to reestablish the temporary platform without impacting the pile portion.
The devices of the present invention are of less complicated structure and less expensive to manufacture, maintain, and operate.